export default {
  bind( el, binding, vnode ) {
    const dialogHeaderEl = el.querySelector( '.el-dialog__header' )
    const dragDom = el.querySelector( '.el-dialog' )
    dialogHeaderEl.style.cssText += ';cursor:move;'
    dragDom.style.cssText += ';top:0px;'

    // 获取原有属性 ie dom元素.currentStyle 火狐谷歌 window.getComputedStyle(dom元素, null);
    const getStyle = ( function() {
      if ( window.document.currentStyle ) {
        return ( dom, attr ) => dom.currentStyle[attr]
      } else {
        return ( dom, attr ) => getComputedStyle( dom, false )[attr]
      }
    } )()

    dialogHeaderEl.onmousedown = ( e ) => {
      // 鼠标按下，计算当前元素距离可视区的距离
      const disX = e.clientX - dialogHeaderEl.offsetLeft
      const disY = e.clientY - dialogHeaderEl.offsetTop

      const dragDomWidth = dragDom.offsetWidth
      const dragDomHeight = dragDom.offsetHeight

      const screenWidth = document.body.clientWidth
      const screenHeight = document.body.clientHeight

      const minDragDomLeft = dragDom.offsetLeft
      const maxDragDomLeft = screenWidth - dragDom.offsetLeft - dragDomWidth

      const minDragDomTop = dragDom.offsetTop
      const maxDragDomTop = screenHeight - dragDom.offsetTop - dragDomHeight

      // 获取到的值带px 正则匹配替换
      let styL = getStyle( dragDom, 'left' )
      let styT = getStyle( dragDom, 'top' )

      if ( styL.includes( '%' ) ) {
        styL = +document.body.clientWidth * ( +styL.replace( /\%/g, '' ) / 100 )
        styT = +document.body.clientHeight * ( +styT.replace( /\%/g, '' ) / 100 )
      } else {
        styL = +styL.replace( /\px/g, '' )
        styT = +styT.replace( /\px/g, '' )
      }

      document.onmousemove = function( e ) {
        // 通过事件委托，计算移动的距离
        let left = e.clientX - disX
        let top = e.clientY - disY

        // 边界处理
        if ( -( left ) > minDragDomLeft ) {
          left = -minDragDomLeft
        } else if ( left > maxDragDomLeft ) {
          left = maxDragDomLeft
        }

        if ( -( top ) > minDragDomTop ) {
          top = -minDragDomTop
        } else if ( top > maxDragDomTop ) {
          top = maxDragDomTop
        }

        // 移动当前元素
        dragDom.style.cssText += `;left:${left + styL}px;top:${top + styT}px;`

        // emit onDrag event
        vnode.child.$emit( 'dragDialog' )
      }

      document.onmouseup = function( e ) {
        document.onmousemove = null
        document.onmouseup = null
      }
    }
  }
}
